mosquito, slow down! It's a generalization, but most new runners run too fast. Their heart rate skyrockets and they have to call it quits. Easy advice would be to start slow, run/walk, PE, blah, blah, blah. Here's one more piece of advice: since you probably already have a HRM, just wear it. Do some heart rate based training.
There's plenty of info available to choose what "zone" to work out in. An article at cool running:
http://www.coolrunning.com/engine/2/2_1/234.shtml
is a good enough place to start.
If you get a nice one, you'll be able to review the data afterwards on your computer. You can analyze how you felt and the corresponding heart rate. Hills will show. Try it on your bike. I bet you're riding with a low heart rate.